( Nearsightedness )
The cause and prevention
by Dr. Somkiat Athikomkullachai
Since 13 April 2005
1. Refractive error that cause deterioration of vision
1.1 Myopia ( Nearsightedness ) is
the most common and increasing problem of vision especially in the
Far-east countries such as Singapore , Taiwan where over 90 %of college
students are nearsighted
Mechanism The eyeball is longer than uaual from front to back. This cause light rays from distant object , focus at a point in front of the retina rather than directly on its surface, resulting in blurred image. This may be hereditary factors or environmental influences or both. It is often discovered in childhood and progresses throughout the teenage years , when the body is growing rapidly.
1.2 Hyperopia ( Farsightedness ) is usually inherited. Most of the
children are mild hyperopia and gradually lessen to normal eyesight
or shift to myopic when they grown up
Mechanism The eyeball is shorter than usual from front to back or
refractive power of the cornea and lens of the eyes is too weak.
rhis cause image formed behind the retina , resulting in a blurred
rision. Most of them can see cleary at distant object through the
process of accommodation ( focusing of the lens in the eyes ) but
mostly blurred vision at near object . If the accommodation is
strong enough they may read or write but not so long that they will
end up with the symptom of tiredness and headache.
1.3 AstigmatismIt is usually inherited , may occur isolately or accompany with myopia or hyperopia
Mechanism It is usually occurs when the front surface of the cornea is not perfectly round. It is steeper in one meridian and flatter in the opposite meridian 180 degrees away. This results in two images forming ( blurred vision ) both distant and near vision
2. Mechanism of near vision
In normal eyesight , light ray from distant object will focus right
on the retina.
When the object move in , the image focus beyond the retina ( blurred vision )
To focus on close object , the ciliary muscle ring must
contract to increase the focusing power and move back the image to the
surface of the retina.
When the ciliary muscle contract , there are 2 things
2.1 The tension of zonule are release and let the lens of the eyes to thicken that increase the focusing power and move in the image behind , to fall on the retina surface.
2.2 The eye is slightly elongated that move out the retina , to meet the image behind
3. Why do children in the city develoop Myopia , more and faster ?
There is more competition in learning at school of the children in the city. When they come home , they live in the building with small room and spend their leisure time in reading , watching T.V. , view on the internet and playing computer game.
The excessive amount of reading , writing and all close work cause the ciliary muscle ring contract almost all the day to focus on close object. Constant focusing on close object cause spasm of the ciliary muscle and constant pulling on the sclera which cause elongation of the eyeball. These children will grown up with the elongated eyeball development ( the myopic eyes )
4. Is Myopia hereditary ?
Yes , because gene will control the shape of the eyeball. Would it be
short from front to back ( Hyperopia ) or be long ( Myopia ) And gene
also control the strength of the scleral layer which is the main structure
to control the shape of the eyeball.
If the sclera is thin and soft , the environment and life style ( affect the ciliary muscle function ) will influence the growth development of the eyeball. But if the sclera is thick and strong , the environment and lifstyle will have less effect.
5. Wearing of Myopic glasses , do any effect to the eyesight
5.1 Myopic child wearing minus or concave glasses for clear distant
vision alike normal eyesight
5.2 Myopic children with glasses , when looking at near object , the
ciliary muscle ring will contract to adjust the lens the same as someone
with normal eyesight But if he put off the eyeglasses to see near
object , the ciliary muscle ring may not necessay to contract or contract
with the lower strength depend upon their myopic power
5.3 Should myopic child wear the glasses all the time from the morning
until bed time ?
No. Myopic child should wear the glasses for seeing distant object
( to relax ciliary muscle ring ) and put off the glasses for seeing
near object ( to lessen the contraction of ciliary muscle ring )
6. Can we prevent Myopia or slow down the progression ?
Yes , sure.
If you have read the mechanism of myopic development above , you will
understand these suggestions
6.1 Initiate your child to see or read the distant object or words
at the billboard anytime you have
6.2 If the child has developed myopia , donít worry. Let your child
correct the vision with myopic glasses. Advise the child to wear glasses
only distant vision and put off when read or do close work.
6.3 Donít let the child to stay with close work all the day such as
reading , watching T.V. or playing computer game but initiate outdoor
6.4 Let the child compress the eyes with 2 palms ,exert the pressure steadily for 60 seconds throughout the orbit for 2 purposes. One is to shorten the eyeball and another is to relax the ciliary muscle ring. Do it once a day at bed time , and after prolonged close work
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